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Author yselivanov
Recipients Ben.Darnell, Yury.Selivanov, asvetlov, gvanrossum, ncoghlan, scoder, vstinner, yselivanov
Date 2015-06-10.02:12:09
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> All this checking for coroutine-ness feels very strange to me. It's anti-duck-typing: [..]

Why is it "anti-duck-typing"?  Awaitable is an object that implements __await__.  With this patch coroutines are a separate type with __await__ (although, ceval doesn't use it to make things faster).

In asyncio we check for "coroutine-ness" only to raise errors if someone passes a wrong object, or to make @asyncio.coroutine work (which will go away eventually).

> Now, not only must it return a generator with the special coroutine flag, the callable itself must be of the right type [..]

Not sure what you mean here.  It doesn't matter what callable is.  It only matters if it returns a native coroutine, a generator-based coroutine, or an object with "__await__".

> Attempting to divide generators into awaitable and non-awaitable subsets is a complex solution to a problem that I'm not convinced is real.

Well, 'await' expression is a new operator, and it makes total sense to limit its usage only to awaitables.  Awaiting on a generator that yields a fibonacci sequence just doesn't make any sense, and *is* error prone.  I think it would be a major mistake to allow this just to make things a little bit more convenient during the transition period.

This particular patch does not divide generators in awaitables and non-awaitables, it introduces a new type for 'async def' coroutines.  All confusion with old generator-based coroutines and @coroutine decorator is here only because we try to be backwards compatible; the compatibility layer can be removed in 3.7 or 3.8.

> Was there a problem in practice with Python 3.4's asyncio in which people used "yield from" in a coroutine with generators that were intended to be iterators instead?

Yes, a lot of people were confused where they have coroutines and where they have generators, and this was even mentioned in the Rationale section of the PEP.
Date User Action Args
2015-06-10 02:12:10yselivanovsetrecipients: + yselivanov, gvanrossum, ncoghlan, scoder, vstinner, asvetlov, Yury.Selivanov, Ben.Darnell
2015-06-10 02:12:10yselivanovsetmessageid: <>
2015-06-10 02:12:10yselivanovlinkissue24400 messages
2015-06-10 02:12:09yselivanovcreate